I have been re-encoding some movies using FFMPEG. I've noticed some movies have the black bars embedded in the video stream, while others don't. Should I keep the black bars in the videos that have them and/or add black bars to the videos that don't have them, or should I use FFMPEG to crop the black bars out? I don't notice any visual difference in any video player I've tested between a film with or without the black bars, so it seems the players are able to display the video properly no matter what.
I know the reason why black bars exist (difference in aspect ratio between movie and display), but I fail to see the purpose of having them baked into the video stream. I know some movies (like the Ghostbusters reboot) use that space for visual effects, and so I wouldn't want to crop movies like that, but otherwise, wouldn't it just be a bunch of wasted storage space otherwise if I kept that padding in, or is there some technical reason why I should leave it?